1. Field of the Invention
The present invention relates to a hybrid drive and a method of operating a hybrid drive.
2. Description of Related Art
Various types of motor vehicles having hybrid drives are known from the related art. Such hybrid drives usually have at least one internal combustion engine and at least one electric machine. The at least one electric machine is able to be individually switched on and off during operation. Furthermore, an additional energy store is provided which is normally one or more batteries and/or accumulators. The electric machine is supplied with electrical energy from the energy store. Conversely, electrical energy is able to be recovered from the electric machine and stored again in the energy store, in response to a so-called braking energy recuperation, for example.
One problem concerning the connection of the at least one internal combustion engine to the at least one electric machine is that, as a rule, a separating clutch and/or a costly transmission has to be provided between these two drive units, in order to be able to operate the different motor(s)/engine(s) independently of one another. Such separating clutches and/or transmissions are costly, however, and heavy, and take up a comparatively large required space. It would therefore be desirable to be able to operate the internal combustion engine in a “stepwise” manner in its operating state. Such “stepwise” operating modes are known from the related art, from the branch of pure combustion engines, and are based on the principle of valve deactivation. Thus, internal combustion engines are already commercially available which may be run in part-load operation, in which not all the cylinders present are operated. Only one-half the number of cylinders is normally operated, in this context. Thus, in V engines, an operating mode is known, for instance, in which one may work by shutting down one bank, since, in such a case, a whole cylinder bank is shut down in a part-load operation. In general, every other cylinder in the ignition sequence is shut down, so that frequently one speaks of an half-engine operation (HEO).
Design attempts are known from the related art that aim to transfer the principle of cylinder cutoff to hybrid drives. Thus, published US patent application 2005/0257967 describes a drive train for a hybrid drive. The hybrid drive has an internal combustion engine having a plurality of cylinders, which in each case have a plurality of deactivatable intake and exhaust valves. The valves are able to be deactivated using a control unit. Consequently, the rotor of the electric motor of the hybrid drive is able to be continuously operatively connected with the crankshaft of the internal combustion engine, so that one may do without a corresponding clutch.
In practice, however, the device shown in published US patent application 2005/0257967 demonstrates a decisive disadvantage which is that, when individual cylinders are deactivated, oil is sucked from the crank housing into the combustion chamber. As a result, when the previously deactivated cylinder is started again, in particular, increased pollutant emission occurs, as well as a transiently deteriorated efficiency.